1. Field of the Invention
The present invention relates to a metal composition for making a conductive film, a metal composition for making an electron emission element, and a method for making the electron emission element and an image forming apparatus using the same.
2. Description of the Related Art
As a cold-cathode electron source, a surface-conduction electron emission element has been known. The surface-conduction electron emission element utilizes the effect of electron emission induced when electric current flows into a small thin film formed on a substrate in a direction parallel to the surface of the film. Examples of the surface-conduction electron emission elements include an element using a SnO2 thin film made by Elinson et al., [M. I., Elinson, Radio Eng. Electron Pys., 10 (1965)], an element using a Au thin layer [G. Dittmer: xe2x80x9cThin Solid Filmsxe2x80x9d, 9,317 (1972)], an element using an In2O3/SnO2 thin film [M. Hartwell and C. G. Fonstad:xe2x80x9cIEEE Trans. ED Conf.xe2x80x9d, 519 (1975)], and an element using a carbon thin film [Hisashi Araki, et al., Shinku, Vol. 26, No. 1, p. 22 (1983)].
With reference to FIG. 6, the configuration of the above-described emitter made by M. Hartwell is described as a typical configuration of a surface-conduction electron emission element. As shown in FIG. 6, the element includes an insulative substrate 1 and a thin film 4 comprising an electron emission section. The electron emission section is made by an electrification process called xe2x80x9cformingxe2x80x9d described below.
In a typical surface-conduction electron emission element, an electron emission section is formed by subjecting a thin film for forming the electron emission section to an electrification process called xe2x80x9cformingxe2x80x9d prior to electron emission. The process of forming includes applying a voltage to the two ends of the thin film 4 using electrodes 2 so as to locally destroy, deform, or degenerate the thin film 4, thereby making an electron emission section having a high electrical resistance. In some cases, a crack would be generated in the thin film during forming, and the vicinity of the crack would function as the electron emission section.
The surface-conduction electron emission element subjected to the above forming process emits electrons from the above-described electron emission section when an electric current flows into the surface of the element by applying a voltage to the thin film 4 comprising the electron emission section.
The thin film 4 including the electron emission section comprises a conductive thin film made by depositing a conductive material on the insulative substrate 1. In a known manufacturing method, the thin film 4 is directly formed on the insulative substrate by deposition such as vacuum evaporation or sputtering of a conductive material. As a less expensive method for making a thin film without using a vacuum apparatus, a thin-film manufacturing method using an inkjet method has been suggested. A water-soluble organic metal compound for preparing an aqueous metal composition and a metal composition for preparing a thin film of excellent quality suitable for the above-described inkjet method are disclosed in Japanese Patent Laid-Open Nos. 8-277294 and 9-185940, respectively.
Furthermore, in order to uniformly form a conductive thin film at a predetermined position of a substrate, a method of preliminarily treating the surface of the substrate has been suggested in Japanese Patent Laid-Open No.10-326559.
In the above methods for forming a conductive thin film using an aqueous organic metal compound and metal composition, desired conductive films are not always formed due to the surface conditions of the substrates on which the metal composition lands, thereby failing to stably provide high-quality elements. Especially, when the substrate surface is preliminarily subjected to water-repellent finishing and thus has a small surface energy, the poor wettability to the metal composition sometimes causes difficulty in manufacturing the conductive thin film.
Accordingly, it is an object of the present invention to provide a metal composition for making a high-quality conductive film.
Another object of the present invention is to provide a metal composition for preparing high-quality conductive film on a surface of a substrate which is subjected to a water-repellent finishing and thus has a small surface energy.
Yet another object of the present invention is to provide a method for making an electron emission element and an image forming apparatus by using the above metal composition.
To achieve these goals, an aspect of the present invention provides a metal composition for making a conductive film, comprising a vinylpyrrolidone-acrylic acid copolymer represented by formula (I): 
wherein x and y are integers.
Another aspect of the present invention provides a metal composition for making an electron emission element, comprising the vinylpyrrolidone-acrylic acid copolymer represented by above formula (I).
Another aspect of the present invention provides a method for making an electron emission element comprising a conductive film for emitting electrons, the method comprising the steps of: providing a metal composition comprising the vinylpyrrolidone-acrylic acid copolymer represented by above formula (I) on a substrate; and baking the metal composition.
Another aspect of the present invention provides a method for making an electron emission element comprising a pair of electrodes opposing each other, and a conductive film disposed between the pair of electrodes, the method comprising the steps of: providing a metal composition comprising the vinylpyrrolidone-acrylic acid copolymer represented by above formula (I) on a region between the pair of electrodes disposed on the substrate; and baking the metal composition.
Yet another aspect of the present invention provides a method for making an image forming apparatus comprising an electron emission element and an image forming unit for forming images by electron irradiation. The electron emission element is made by any one of the methods described above.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments (with reference to the attached drawings).